A method and an apparatus for continuous real-time tracking of the position of at least one mobile transmitter is known from EP 1 556 713 B1, wherein a plurality of receivers of a stationary receiver and signal processing network receive the signals emitted by the transmitter. Times of traveling, or what are known as TOA (time of arrival) values, are determined between the transmitter and each of the receivers from the receiver signals, wherein, for example with 12 TOA values from 12 stationary receivers, 11 time differences, or what are known as TDOA (time difference of arrival) values, are formed by reference to one of the receivers, from which the respective position of the transmitter is calculated by hyperbolic triangulation, which is implemented in a Kalman filter. This method and this apparatus have been used for example for real-time tracking of a ball and/or of players on a playing field, for example, on a football field.
With such a known system, a rotating mobile transmitter, which for example is arranged in a ball, generates distorted carrier phase measured values, which then distort the position result for the transmitter. This interference increases as the ball rotates faster. This effect can be attributed to the selection of the antennas used. The transmitter emits linearly polarized waves, as is also the case, for example, with a linear dipole. Circularly polarized antennas are used on the receiver side, wherein the plane of polarization is also rotated by the rotation of the ball or of the transmitter, which is perceived at the receiver as a shift in the carrier frequency. The measured values of the carrier phase derived from the carrier frequency are distorted by this interference effect and are therefore no longer a reliable measured quantity for the distance or change thereto. If the measured carrier phase values are taken into account in the position calculation, this results in a position error to a greater or lesser extent. To solve this problem, it is possible to dispense with the carrier phase measurement or the carrier phase measured values in the position calculation, however the positional result would then be considerably impaired, since only the relatively inaccurate code phase measurement of the Traveling times of the signals would be used.
The physical effect occurring in conjunction with the cited prior art is also present in other systems, for example in the GPS system, wherein, in the GPS system, the error is eliminated since the phase difference is formed between the measured values of two satellites. A precondition in this case is that the receiving antenna is only rotated about the vertical axis, which is generally the case. In the localization method according to the above-cited prior art, the transmitter rotates completely randomly, which is why the compensation of the error applied with the GPS system is not possible.
A further prior art in which the aforementioned physical effect is used for the orientation measurement is U.S. Pat. No. 3,540,045, in which the alignment of the plane of polarization in the satellite communication is established and controlled. In this case, the angle of the plane of polarization of a satellite signal is measured using a turnstile antenna, which can simultaneously receive right-hand and left-hand circularly polarized electromagnetic field components. U.S. Pat. No. 7,123,187 is used to determine the alignment of a GPS receiver, wherein a “standard GPS antenna configuration” is used, that is to say a right-hand circularly polarised antenna at the transmitter and receiver. In this case, two carrier frequencies of the GPS system are used, wherein the two components can be determined or separated from the different phase changes during rotation, during which both phase measured values change in a similar manner, and from the change in distance, with which the phase changes are dependent on the respective wavelength.